Last year I went to my first haunted house with my girlfriend (we broke up though)
Don't worry about being a chicken, I HATE scary stuff, and I had a blast. They are designed and MEANT to scare you. And if you get scared, SING. My girlfriend thought it was the funniest thing, because I started singing in my group of 5 through the haunted corn maze. I sang 99 bottles of beer on the wall. You know what happened? ALL of the people working in the maze sang WITH us, and it almost turned into a chant for that maze.
It really isn't anything worth getting all crazy worried over. Worst case scenario is you scream like a little girl and have a good laugh (unless you have bladder malfunctions when someone in a costume screams at you from 3 feet away. Then you should probably claim you caught the flu on the day of the trip.)
Good luck to you